Repositionable endoluminal support structure and its applications

ABSTRACT

An endoluminal support structure includes strut members interconnected by swivel joints to form a series of linked scissor mechanisms. The structure can be remotely actuated to compress or expand its shape by adjusting the scissor joints within a range of motion. In particular, the support structure can be repositioned within the body lumen or retrieved from the lumen. The support structure can be employed to introduce and support a prosthetic valve within a body lumen.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/761,295, filed on Apr. 15, 2010, now U.S. Pat. No. 8,226,707 which isa continuation of PCT Application No. PCT/US2009/051324, filed on Jul.21, 2009, which claims the benefit of U.S. Provisional Application No.61/082,489, filed on Jul. 21, 2008, all of which are hereby incorporatedby reference in their entirety.

BACKGROUND

Endoluminal stents can be implanted in a vessel or tract of a patient tohelp maintain an open lumen. The stents can also be used as a frame tosupport a prosthetic device or to deliver a therapeutic agent. Stentscan be implanted by either an open operative procedure or a closedoperative procedure. When an option exists, the less invasive closedprocedure is generally preferred because the stent can be guided througha body lumen, such as the femoral artery, to its desired location.

Closed procedures typically use one of two techniques. One closedprocedure employs balloon catheterization where an expandable stentencloses an inflatable balloon. In this procedure, the stent isimplanted by inflating the balloon, which causes the stent to expand.The actual positioning of the stent cannot be determined until after theballoon is deflated and, if there is a misplacement of the stent, theprocess cannot be reversed to reposition the stent.

The other closed procedure employs a compressed stent enclosed by aremovable sheath. In this procedure, a stent made from a shape memoryalloy, such as Nitinol, is held in a compressed state by a sheath. Thestent is implanted by withdrawing the sheath, causing the stent toexpand to its nominal shape. Again, if there is a misplacement of thestent, the process cannot be reversed to reposition the stent.

Positioning errors are particularly dangerous when the stent is used tosupport a cardiac valve. Serious complications and patient deaths haveoccurred due to malpositioning of the valve at the implant site in thebody, using the available stent-mounted valves. Malpositioning of thevalve has resulted in massive paravalvular leakage, device migration,and coronary artery obstruction. The majority of these complicationswere unavoidable, but detected at the time of the procedure. However,due to inability to reposition or retrieve the device, these problemswere impossible to reverse or mitigate during the procedure.

SUMMARY

An endoluminal support structure or stent in accordance with certainembodiments of the invention solves certain deficiencies found in theprior art. In particular, the support structure can be repositionedwithin the body lumen or retrieved from the lumen.

A particular embodiment of the invention includes a support apparatusimplantable within a biological lumen. The support apparatus can includea plurality of elongated strut members interlinked by a plurality ofswivel joints, wherein the swivel joints can cooperate with the stentmembers to adjustably define a shaped structure between a compressedorientation and an expanded orientation.

More particularly, the shaped structure can be one of a cylindrical, aconical, or an hourglass shape. A swivel joint can form a scissormechanism with a first strut member and a second strut member.Furthermore, the strut members can be arranged as a series of linkedscissor mechanisms. The apparatus can further include an actuationmechanism to urge the swivel joints within a range of motion.

The apparatus can also include a prosthetic valve coupled to the shapedstructure.

Another particular embodiment of the invention can include a medicalstent implantable within a biological lumen. The medical stent caninclude a plurality of elongated strut members, including a first strutmember and a second strut member, and a swivel joint connecting thefirst strut member and the second strut member.

In particular, the swivel joint can form a scissor mechanism with thefirst strut member and the second strut member. The swivel joint canbisect the first strut member and the second strut member. The swiveljoint can interconnect a first end of the first strut member with afirst end of the second strut member.

The plurality of strut members can be arranged as a series of linkedscissor mechanisms. The strut members can also be non-linear. The strutmembers can be arranged to form one of a cylindrical, a conical, or anhourglass shape.

The stent can further include an adjustment mechanism to exerting aforce to urge the strut members about the swivel joint within a range ofmotion.

The stent can include a prosthetic valve coupled to the strut members.

Specific embodiments of the invention can include prosthetic valves thatare rotatable or conventional.

A rotatable prosthetic valve can include a first structural membercoupled to the strut members, a second structural member rotatablerelative to the first structural member, and a plurality of pliablevalve members connecting the first structural member with the secondstructural member such that rotation of the second structural memberrelative to the first structural member can urge the valve membersbetween an open and a closed state. In particular, the rotation of thesecond structural member can be responsive to the natural flow of abiological fluid.

A conventional prosthetic valve can include a plurality of pliable valveleaflets having commissures at the intersection of two strut members.The prosthetic valve can further include a skirt material coupled to thestrut members.

A particular advantage of a support structure in accordance withembodiments of the invention is that it enables a prosthetic valve to bereadily retrieved and repositioned in the body. If following deployment,the valve is malpositioned or deemed dysfunctional, the supportstructure allows the valve to be readily repositioned and re-deployed ata new implant site, or removed from the body entirely. This feature ofthe device can prevent serious complications and save lives by enablingthe repair of mal-positioned devices in the body.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of particular embodiments of the invention, as illustratedin the accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a perspective view of a particular endoluminal supportstructure.

FIG. 2 is a perspective view of a four strut section of the stent ofFIG. 1.

FIG. 3 is a perspective view of a compressed support structure of FIG.1.

FIG. 4 is a perspective view of the support structure of FIG. 1 in afully expanded state.

FIG. 5 is a perspective view of the support structure of FIG. 2 having aparticular actuator mechanism.

FIG. 6 is a perspective view of the support structure of FIG. 2 havinganother particular actuator mechanism.

FIG. 7 is a perspective view of a particular support structure andcontrol catheter assembly usable with the actuator mechanisms of FIGS. 5and 6.

FIG. 8 is a perspective view of a particular rotating prosthetic valveassembly.

FIG. 9 is a perspective view of the valve assembly of FIG. 8 while beingclosed.

FIG. 10 is a perspective view of the valve assembly of FIG. 8 oncecompletely closed.

FIG. 11 is a perspective view of the valve of FIGS. 8-10 in combinationwith the support structure of FIG. 1.

FIG. 12 is a perspective view of the valve of FIG. 11 in the openposition.

FIG. 13 is a perspective view of a traditional tissue valve mounted tothe support structure of FIG. 1.

FIG. 14 is a perspective view of the valve structure of FIG. 13 having afull inner skirt.

FIG. 15 is a perspective view of the valve structure of FIG. 13 having afull outer skirt.

FIG. 16 is a perspective view of the arrangement of strut members in aconical-shaped support structure configuration.

FIG. 17 is a perspective view of an hourglass-shaped support structureconfiguration.

DETAILED DESCRIPTION

Particular embodiments of the invention include endoluminal supportstructures (stents) and prosthetic valves.

FIG. 1 is a perspective view of a particular endoluminal supportstructure. As shown, the support structure 10 is a medical stent thatincludes a plurality of longitudinal strut members 11 interconnected bya plurality of swivel joints 15. In particular, the swivel joints 15allow the interconnected strut members 11 to rotate relative to eachother. As shown, there are eighteen struts 11.

The strut members 11 are fabricated from a rigid or semi-rigidbiocompatible material, such as plastics or other polymers and metalalloys, including stainless steel, tantalum, titanium, nickel-titanium(e.g. Nitinol), and cobalt-chromium (e.g. ELGILOY). The dimensions ofeach strut can be chosen in accordance with its desired use. In aparticular embodiment, each strut member is made from stainless steel,which is 0.005-0.020 inch thick. More particularly, each strut is 0.010inch thick 300 series stainless steel. While all struts 11 are shown asbeing of uniform thickness, the thickness of a strut can vary across astrut, such as a gradual increase or decrease in thickness along thelength of a strut. Furthermore, individual struts can differ inthickness from other individual struts in the same support structure.

As shown, each strut member 11 is bar shaped and has a front surface 11f and a back surface 11 b. The strut members can however be of differentgeometries. For example, instead of a uniform width, the struts can varyin width along its length. Furthermore, an individual strut can have adifferent width than another strut in the same support structure.Similarly, the strut lengths can vary from strut to strut within thesame support structure. The particular dimensions can be chosen based onthe implant site.

Furthermore, the struts can be non-flat structures. In particular, thestruts can include a curvature, such as in a concave or convex manner inrelationship to the inner diameter of the stent structure. The strutscan also be twisted. The nonflatness or flatness of the struts can be aproperty of the material from which they are constructed. For example,the struts can exhibit shape-memory or heat- responsive changes in shapeto the struts during various states. Such states can be defined by thestent in the compressed or expanded configuration.

Furthermore, the strut members 11 can have a smooth or rough surfacetexture. In particular, a pitted surface can provide tensile strength tothe struts. In addition, roughness or pitting can provide additionalfriction to help secure the support structure at the implant site andencourage irregular encapsulation of the support structure 10 by tissuegrowth to further stabilize the support structure 10 at the implant siteover time.

In certain instances, the stent could be comprised of struts that aremultiple members stacked upon one another. Within the same stent, somestruts could include elongated members stacked upon one another in amulti-ply configuration, and other struts could be one-ply, composed ofsingle-thickness members. Within a single strut, there can be areas ofone-ply and multi-ply layering of the members.

Each strut member 11 also includes a plurality of orifices 13 spacedalong the length of the strut member 11. On the front surface 11 f, theorifices are countersunk 17 to receive the head of a fastener. In aparticular embodiment, there are thirteen equally spaced orifices 13along the length of each strut member 11, but more or less orifices canbe used. The orifices 13 are shown as being of uniform diameter anduniform spacing along the strut member 11, but neither is required.

The strut members 11 are arranged as a chain of four-bar linkages. Thestrut members 11 are interconnected by swivelable pivot fasteners 25,such as rivets, extending through aligned orifices 13. It should beunderstood that other swivelable fasteners 25 can be employed such asscrews, bolts, ball-in-socket structures, nails, or eyelets, and thatthe fasteners can be integrally formed in the struts 11 such as a peenedsemi-sphere interacting with an indentation or orifice, or a male-femalecoupling. In addition to receiving a fastener, the orifices 13 alsoprovide an additional pathway for tissue growth-over to stabilize andencapsulate the support structure 10 over time.

FIG. 2 is a perspective view of a four strut section of the stent ofFIG. 1. As shown, two outer strut members 11-1, 11-3 overlap two innerstrut members 11-2, 11-4, with their back surfaces in communication witheach other.

In particular, the first strut member 11-1 is swivelably connected tothe second strut member 11-1 by a middle swivel joint 15-1 using a rivet25-1, which utilizes orifices 13 that bisect the strut members 11-1,11-2. Similarly, the third strut member 11-3 is swivelably connected tobisect the fourth strut member 11-4 by a middle swivel joint 15-7 usinga rivet 25-7. It should be understood that the middle swivel joints15-1, 15-7 function as a scissor joint in a scissor linkage ormechanism. As shown, the resulting scissor arms are of equal length. Itshould also be understood that the middle joint 15-1, 15-7 need notbisect the joined strut members, but can instead utilize orifices 13offset from the longitudinal centers of the strut members resulting inunequal scissor arm lengths.

In addition to the middle scissor joint 15-1, the first strut member11-1 is swivelably connected to the third strut member 11-3 by a distalanchor swivel joint 15-5, located near the distal ends of the strutmembers 11-1, 11-3. Similarly, the first strut member 11-1 is swivelablyconnected to the fourth strut member 11-4 by a proximal anchor swiveljoint 15-3, located near the proximal ends of the strut members 11-1,11-4. To reduce stresses on the anchor rivets 25-3, 25-5, the distal andproximal ends of the struts 11 can be curved or twisted to provide aflush interface between the joined struts.

As can be seen, the support structure 10 (FIG. 1) is fabricated bylinking together a serial chain of scissor mechanisms. The chain is thenwrapped to join the last scissor mechanism with the first scissormechanism in the chain. By actuating the linkage the links can be openedor closed, which results in expanding or compressing the stent 10 (FIG.1).

Returning to FIG. 1, by utilizing the swivel joints 15, the diameter ofthe stent can be compressed for insertion through a biological lumen,such as an artery, to a selected position. The stent can then beexpanded to secure the stent at the selected location within the lumen.Furthermore, after being expanded, the stent can be recompressed forremoval from the body or for repositioning within the lumen.

FIG. 3 is a perspective view of a compressed support structure ofFIG. 1. When compressed, the stent 10 is at its maximum length andminimum diameter. The maximum length is limited by the length of thestrut members, which in a particular embodiment is 15 mm. The minimumdiameter is limited by the width of the strut members, which in aparticular embodiment is 0.052 inch.

FIG. 4 is a perspective view of the support structure of FIG. 1 in afully expanded state. As shown, the fully expanded support structure 10forms a ring, which can be used as an annuloplasty ring. In particular,if one end of the stent circumference is attached to tissue, thecompression of the stent will enable the tissue to cinch. Because thestent has the ability to have an incremental and reversible compressionor expansion, the device could be used to provide an individualizedcinching of the tissue to increase the competency of a heart valve. Thiscould be a useful treatment for mitral valve diseases, such as mitralregurgitation or mitral valve prolapse.

While the support structure 10 can be implanted in a patient during anopen operative procedure, a closed procedure will often be moredesirable. As such, the support structure 10 can include an actuationmechanism to allow a surgeon to expand or compress the support structurefrom a location remote from the implant site. Due to the properties of ascissor linkage wrapped into a cylinder (FIG. 1), actuation mechanismscan exert work to expand the stent diameter by either increasing thedistance between neighboring scissor joints, and decreasing the distancebetween the anchor joints.

FIG. 5 is a perspective view of the support structure of FIG. 2 having aparticular actuator mechanism. As shown, the actuator mechanism 30includes a dual-threaded rod 32 positioned on the inside of the supportstructure 10 (FIG. 1). It should be understood, however, that theactuator mechanism 30 can instead be positioned on the outside of thesupport structure 10. Whether positioned on the inside or outside, theactuator mechanism 30 operates in the same way. The rod includesright-hand threads 34R on its proximal end and left-hand threads 34L onits distal end. The rod 32 is mounted the anchor points 15-3, 15-5 usinga pair of threaded low-profile support mounts 35-3, 35-5. Each end ofthe rod 32 is terminated by a hex head 37-3, 37-5 for receiving a hexdriver (not shown). As should be understood, rotating the rod 32 in onedirection will urge the anchor points 25-3, 25-5 outwardly to compressthe linkages while rotating the rod 32 in the opposite direction willurge the anchor points 25-3, 25-5 inwardly to expand the linkages.

FIG. 6 is a perspective view of the support structure of FIG. 2 havinganother particular actuator mechanism. As shown, the actuator mechanism30′ includes a single-threaded rod 32′ positioned on the inside of thesupport structure 10 (FIG. 1). The rod 32′ includes threads 34′ on oneof its ends. The rod 32′ is mounted to lowprofile anchor points 15-3,15-5 using a pair of support mounts 35′-3, 35′-5, one of which isthreaded to mate with the rod threads 34′. The unthreaded end of the rod32′ includes a retaining stop 39′ that bears against the support mount35′-5 to compress the support structure. Each end of the rod 32′ isterminated by a hex head 37′-3, 37′-5 for receiving a hex driver (notshown). Again, rotating the rod 32′ in one direction will urge theanchor points 25-3, 25-5 outwardly to compress the linkages whilerotating the rod 32′ in the opposite direction will urge the anchorpoints 25-3, 25-5 inwardly to expand the linkages.

In addition, because the struts overlap, a ratcheting mechanism can beincorporated to be utilized during the sliding of one strut relative tothe other. For example, the stent could lock at incremental diametersdue to the interaction of features that are an integral part of eachstrut. An example of such features would be a male component (e.g.bumps) on one strut surface which mates with the female component (e.g.holes) on the surface of the neighboring strut surface, as the twostruts slide pass one another. Such structures could be fabricated tohave an orientation, such that they incrementally lock the stent in theexpanded configuration as the stent is expanded. Such a stent could beexpanded using a conventional balloon or other actuation mechanismdescribed in this application.

Because the support structure 10 of FIGS. 5 and 6 are intended to beimplanted during a closed surgical procedure, the actuator mechanism iscontrolled remotely by a surgeon. In a typical procedure, the supportstructure 10 is implanted through a body lumen, such as the femoralartery using a tethered endoluminal catheter. As such, the actuatormechanism 30 can be controlled via the catheter.

FIG. 7 is a perspective view of a particular support structure andcontrol catheter assembly usable with the actuator mechanisms of FIGS. 5and 6. The control catheter 40 is dimensioned to be inserted with thesupport structure through a biological lumen, such as a human artery. Asshown, the control catheter 40 includes a flexible drive cable 42 havinga driver 44 on its distal end that removably mates with a hex head 37,37′ of the actuator mechanism (FIGS. 5 and 6). The proximal end of thecable 42 includes a hex head 46. In operation, the proximal hex head 46of the cable 42 is rotated by a surgeon, using a thumb wheel or othersuitable manipulator (not shown). Rotation of the hex head 46 istransferred by the cable 42 to the driver head 44 to turn the actuatorrod 30, 30′ (FIGS. 5 and 6).

The cable 42 is encased by a flexible outer sheath 48. The distal end ofthe outer sheath 48 includes a lip or protuberance 49 shaped tointerface with the support structure 10. When the cable 42 is turned,the outer sheath lip 49 interacts with the support structure 10 tocounteract the resulting torque.

By employing threads, the rod is self-locking to maintain the supportstructure in the desired diameter. In a particular embodiment, the rod32, 32′ has a diameter of 1.0 mm and a thread count of 240 turns/inch.While a threaded rod and drive mechanism are described, other techniquescan be employed to actuate the linkages depending on the particularsurgical application. For example, the actuator mechanism can bedisposed within the thickness of the strut members, instead of inside oroutside of the stent. For example, worm gears or a rack and pinionmechanism can be employed as known in the art. One of ordinary skill inthe art should recognize other endoluminal actuation techniques. Inother situations, the support structure can be implanted during an openprocedure, which may not require an external actuation mechanism.

Although there are other uses for the described support structure, suchas drug delivery, a particular embodiment supports a prosthetic valve.In particular, the support structure is used in combination with aprosthetic valve, such as for an aortic valve replacement.

FIG. 8 is a perspective view of a particular rotating prosthetic valveassembly. The prosthetic valve 100 comprises a three leafletconfiguration shown in an open position. The leaflets are derived from abiocompatible material, such as animal pericardium (e.g. bovine,porcine, equine), human pericardium, chemically treated pericardium,gluteraldehyde-treated pericardium, tissue engineered materials, ascaffold for tissue engineered materials, autologous pericardium,cadaveric pericardium, Nitinol, polymers, plastics, PTFE, or any othermaterial known in the art.

The leaflets 101 a, 101 b, 101 c are attached to a stationarycylindrical member 105 and a non-stationary cylindrical member 107. Oneside of each leaflet 101 is attached to the non-stationary cylindricalmember 107. The opposing side of each leaflet 101 is attached to thestationary cylindrical member 105. The attachment of each leaflet 101 isin a direction generally perpendicular to the longitudinal axis of thecylindrical members 105, 107. In this embodiment, each leaflet 101 ispliable, generally rectangular in shape, and has a 180 degree twistbetween its attachments to stationary member 105 and non-stationarymember 107. Each leaflet 101 has an inner edge 102 and an outer edge103, with the edges 102 c, 103 c of one leaflet 101 c being referencedin the figure. As known in the art, the leaflets can be fabricated fromeither biological or non-biological materials, or a combination of both.

One way to actuate the valve to close is by utilizing the forces exertedby the normal blood flow or pressure changes of the cardiac cycle. Morespecifically, the heart ejects blood through the fully open valve in thedirection of the arrow shown in FIG. 8. Shortly thereafter, the distalor downstream blood pressure starts to rise relative to the proximalpressure across the valve, creating a backpressure on the valve.

FIG. 9 is a perspective view of the valve assembly of FIG. 8 while beingclosed. That backpressure along the direction of the arrow causes theaxially displacement of the leaflets 101 and non-stationary member 107towards the stationary cylindrical member 105. As the leaflets 101 movefrom a vertical to horizontal plane relative to the longitudinal axis, anet counter-clockwise torque force is exerted on the non-stationarymember 107 and leaflets 101. The torque force exerts a centripetal forceon the leaflets 101.

FIG. 10 is a perspective view of the valve assembly of FIG. 8 oncecompletely closed. Complete closure of the valve 100 occurs as theleaflets 101 displace to the center of the valve and the non-stationarycylindrical member 107 rests upon the stationary member 105, as shown.

The function of the valve 100 opening can be understood by observing thereverse of the steps of valve closing, namely following the sequence ofdrawings from FIG. 10 to FIG. 8.

In considering the valve 100 as an aortic valve replacement, it wouldremain closed as shown in FIG. 10, until the heart enters systole.During systole, as the myocardium forcefully contracts, the bloodpressure exerted on the valve's proximal side (the side closest to theheart) is greater than the pressure on the distal side (downstream) ofthe closed valve. This pressure gradient causes the leaflets 101 andnon-stationary cylindrical member 107 to displace away from thestationary member 105 along the axial plane. The valve 100 brieflyassumes the half-closed transition state shown in FIG. 9.

As the leaflets 101 elongate from a horizontal to vertical orientationalong the axial plane, a net torque force is exerted on the leaflets 101and non-stationary cylindrical member 107. Since the valve 100 isopening, as opposed to closing, the torque force exerted to open thevalve is opposite to that exerted to close the vlave. Given theconfiguration of embodiment shown in FIG. 9, the torque force that opensthe valve would be in clockwise direction.

The torque forces cause the leaflets 101 to rotate with thenon-stationary member 107 around the longitudinal axis of the valve 100.This, in turn, exerts a centrifugal force on each leaflet 101. Theleaflets 101 undergo radial displacement away from the center,effectively opening the valve and allowing blood to flow away from theheart, in the direction shown by the arrow in FIG. 8.

To summarize, the valve passively functions to provide unidirectionalblood flow by linking three forces. Axial, torque, and radial forces aretranslated in a sequential and reversible manner, while encoding thedirectionality of prior motions. First, the axial force of blood flowand pressure causes the displacement of the leaflets 101 andnon-stationary members 107 relative to the stationary member 105 alongthe axial plane. This is translated into a rotational force on theleaflets 101 and non-stationary member 107. The torque force, in turn,displaces the leaflets 101 towards or away from the center of the valve,along the radial plane, which closes or opens the valve 100. The valve100 passively follows the pathway of opening or closing, depending onthe direction of the axial force initially applied to the valve by thecardiac cycle.

In the body, the stationary cylindrical member 105 can secured and fixedin position at the implant site, while the non-stationary member 107 anddistal ends of leaflets 101 are free to displace along the axial plane.In using the prosthetic valve as an aortic valve replacement, thestationary member 105 would be secured in the aortic root. As the bloodpressure or flow from the heart, increases, the valve 100 changes fromits closed configuration to the open configuration, with blood ejectingthrough the valve 100.

Specific advantages of the rotating valve of FIGS. 8-10, along withfurther embodiments, are described in the above-incorporated parentprovisional patent application.

FIG. 11 is a perspective view of the valve of FIGS. 8-10 in combinationwith the support structure of FIG. 1. As shown in the closed position,the valve's stationary member 105 is attached to the support structure10. The valve's nonstationary member 107 is not attached to the supportstructure 10. This enables the non-stationary member 107 to displacealong the axial plane along with the leaflets 101 during valve openingor closing. In this particular embodiment, the valve 100 occupies aposition that is closer to one end of the support structure 10, asshown.

FIG. 12 is a perspective view of the valve of FIG. 11 in the openposition. As noted above, the non-stationary member 107 is not attachedto support structure 10, and is thus free to displace along the axialplane, along with the leaflets 101. In this particular embodiment,during full opening, non-stationary member 107 and the leaflets 101remain within the confines of the support structure 10.

The stented valve 110 can be implanted during a closed procedure asdescribed above. However, because of the operation of the non-stationarymember within the body of the stent, the actuator mechanism to compressand expand the stent would not be disposed within the stent.

Further embodiments of the stented valve 110, positioning of the valvein the body, and procedures for implantation are described in theabove-incorporated parent provisional patent application. In addition, atissue valve can be draped on the support structure. Additionalembodiments should be apparent to those of ordinary skill in the art.

FIG. 13 is a perspective view of a traditional tissue valve mounted tothe support structure of FIG. 1. As shown, a stented valve 120 includesa prosthetic tissue valve 121 attached to a support structure 10, suchas that described above.

The tissue valve 121 includes three pliable semi-circular leaflets 121a, 121 b, 121 c, which can be derived from biocompatible materials asnoted with reference to FIG. 8. Adjacent leaflets are attached in pairsto commissures 123 x, 123 y, 123 z on the support structure 10. Inparticular, the commissures 123 x, 123 y, 123 z correspond withspaced-apart distal anchor points 13 x, 13 y, 13 z on the supportstructure 10. In an 18-strut stent, the commissures are attached thestructure 10 via corresponding fasteners 25 at every third distal anchorpoint.

From the commissures, the leaflet sides are connected to the adjacentdiagonal struts. That is, the sides of the first leaflet 121 a aresutured to the struts 11-Xa and 11-Za, respectively; the sides of thesecond leaflet 121 b are sutured to the struts 11-Xb and 11-Yb,respectively; and the sides of the third leaflet 121 c are sutured tothe struts 11-Yc and 11-Zc, respectively. Those sutures end at thescissor pivot points on the diagonal struts.

In the configuration shown, neighboring struts 11 are attached to oneanother in a manner that creates multiple arches 128 at the ends of thestent. Posts for leaflet attachment, or commissures, are formed byattaching neighboring leaflet to each of the struts that define asuitable arch 128 x, 128 y, 128 z. In the configuration shown, there arethree leaflets 121 a, 121 b, 121 c, each of which is attached to a strutalong two of its opposing borders. The commissures are formed by threeequi-distance arches 128 x, 128 y, 128 z in the stent.

The angled orientation of a strut in relationship to its neighboringstrut enables the leaflets 121 a, 121 b, 121 c to be attached to thestent in an triangular configuration. This triangular configurationsimulates the angled attachment of the native aortic leaflet. In thenative valve this creates an anatomical structure between leaflets,known as the inter-leaflet trigone. Because the anatomical inter-leaflettrigone is believed to offer structural integrity and durability to thenative aortic leaflets in humans, it is advantageous to simulate thisstructure in a prosthetic valve.

One method of attachment of the leaflets to the struts is to sandwichthe leaflet between a mutli-ply strut. The multiple layers are then heldtogether by sutures. Sandwiching the leaflets between the struts helpsto dissipate the forces on leaflets and prevent the tearing of suturesthrough the leaflets.

The remaining side of each leaflet 121 a, 121 b, 121 c is suturedannularly across the intermediate strut members as shown by a leafletseam. The remaining open spaces between the struts are draped by abiocompatible skirt 125 to help seal the valve against the implant siteand thus limit paravalvular leakage. As shown, the skirt 125 is shapedto cover those portions of the stent below and between the valveleaflets.

In more detail, the skirt 125 at the base of the valve is a thin layerof material that lines the stent wall. The skirt material can bepericardial tissue, polyester, PTFE, or other material or combinationsof materials suitable for accepting tissue in growth, includingchemically treated materials to promote tissue growth or inhibitinfection. The skirt layer functions to reduce or eliminate leakagearound the valve, or “paravalvular leak”. To that end, there are anumber of ways to attach the skirt material layer to the stent,including:

-   -   the skirt layer can be on the inside or the outside of the        stent;    -   the skirt layer can occupy the lower portion of the stent;    -   the skirt layer can occupy the lower and upper portion of the        stent;    -   the skirt layer can occupy only the upper portion of the stent;    -   the skirt layer can occupy the area between the struts that        define the commissure posts;    -   the skirt layer can be continuous with the leaflet material;    -   the skirt layer can be sutured to the struts or a multitude of        sites; or    -   the skirt layer can be secured to the lower portion of the        stent, and pulled or pushed up to cover the outside of the stent        during the deployment in the body.

The above list is not necessarily limiting as those of ordinary skill inthe art may recognize alternative draping techniques for specificapplications.

FIG. 14 is a perspective view of the valve structure of FIG. 13 having afull inner skirt. A stented valve 120′ includes a prosthetic tissuevalve 121′ having three leaflets 121 a′, 121 b′, 121 c′ attached to asupport structure 10. A skirt layer 125′ covers the interior surface ofthe stent 10. As such, the valve leaflets 121 a′, 121 b′, 121 c′ aresutured to the skirt layer 125′.

FIG. 15 is a perspective view of the valve structure of FIG. 13 having afull outer skirt. A stented valve 120″ includes a prosthetic tissuevalve 121″ having three leaflets 121 a″, 121 b″, 121 c″ attached to asupport structure 10, such as that described in FIG. 13. A skirt layer125″ covers the exterior surface of the stent 10.

The tissue valve structures 120, 120′, 120″ can also be implanted duringa closed procedure as described above. However, the actuator mechanismto compress and expand the stent would be attached to avoid thecommissure points and limit damage to the skirt layer 125, 125′, 125″,such as by mounting the actuator mechanism on the outer surface of thestent 10.

While the above-described embodiments have featured a support structurehaving linear strut bars and equal length scissor arms, other geometriescan be employed. The resulting shape will be other than cylindrical andcan have better performance in certain applications.

FIG. 16 is a perspective view of the arrangement of strut members in aconical-shaped support structure configuration. In the conical structure10′, the strut members 11 are arranged as shown in FIG. 2, except thatthe middle scissor pivots do not bisect the struts. In particular, themiddle scissor pivots (e.g. 15′-1, 15′-7) divide the joined strutmembers (e.g. 11′-1, 11′-2 and 11′-3, 11′4) into unequal segments of5/12 and 7/12 lengths. When fully assembled, the resulting supportstructure thus conforms to a conical shape when expanded. Forillustration purposes, the stent 10′ is shown with a single-threadedactuator rod 32′ (FIG. 6), but it is not a required element for thisstent embodiment.

The stent 10′ can also assume a cone shape in its expanded configurationby imposing a convex or concave curvature to the individual strutmembers 11 that comprise the stent 10′. This could be achieved by usinga material with memory, such as shape-memory or temperature sensitiveNitinol.

A valve can be orientated in the cone-shaped stent 10′ such that thebase of the valve was either in the narrower portion of the cone-shapedstent, with the nonbase portion of the valve in the wider portion of thecone. Alternatively, the base of the valve can be located in the widestportion of the stent with the non-base portion of the valve in theless-wide portion of the stent.

The orientation of a cone-shaped stent 10′ in the body can be eithertowards or away from the stream of blood flow. In other body lumens(e.g. respiratory tract or gastrointestinal tract), the stent could beorientated in either direction, in relationship to the axial plane.

FIG. 17 is a perspective view of an hourglass-shaped support structureconfiguration. In this configuration, the circumference around themiddle pivot points 15″-1, 15″-7, 15″-9 (the waist) is less than thecircumference at either end of the stent 10″. As shown, the hourglassshaped support structure 10″ is achieved by reducing the number of strutmembers 11″ to six and shortening the strut members 11″ in comparison toprior embodiments. As a result of the shortening, there are fewerorifices 13″ per strut member 11″. Because of the strut number andgeometry, each strut member 11″ includes a twist at points 19″ alongthere longitudinal planes. The twists provide a flush interface betweenjoined strut 15″-3.

An hourglass stent configuration could also be achieved by imposingconcave or convex curvatures in individual bars 11″. The curvature couldbe a property of the materials (e.g. shape-memory or heat-sensitiveNitinol). The curvature could be absent in the compressed stent stateand appear when the stent is in its expanded state.

It should be noted that any of the above-described support structurescan be extended beyond the anchor joints at either of both ends of thestent. By coupling a series of stents in an end-to-end chain fashion,additional stent lengths and geometries can be fabricated. Inparticular, an hourglass-shaped stent could be achieved by joining twocone-shaped stents at their narrow ends. The hourglass shape can also bemodified by assembling the middle scissor pivots off center as shown inFIG. 14.

Particular embodiments of the invention offer distinct advantages overthe prior art, including in their structure and applications. Whilecertain advantages are summarized below, the summary is not necessarilya complete list as there may be additional advantages.

The device allows the user to advert the serious complications that canoccur during percutaneous heart valve implantation. Because the deviceis retrievable and re-positionable during implantation into the body,the surgeon can avoid serious complications due to valve malpositioningor migration during implantation. Examples of these complicationsinclude occlusion of the coronary arteries, massive paravalvularleakage, or arrthymias.

The device can also decrease vascular access complications because ofthe device's narrow insertion profile. The device's profile is low, inpart, due to its unique geometry, which allows neighboring struts in thestent to overlap during stent compression. The device's low profile isfurther augmented by eliminating the necessity for a balloon or asheath. The device's narrow profile offers the advantage of widening thevascular access route options in patients. For instance, the device canenable the delivery of the prosthetic valve through an artery in the legin a patient whom would have previously been committed to a moreinvasive approach through the chest wall. The device therefore aims todecrease complications associated with the use of large profile devicesin patients with poor vascular access.

The tissue valve embodiments can offer improved durability by allowingfor attachment of the leaflets to flexible commissural posts. Theflexible posts allow dissipation of the stress and strain imposed on theleaflet by the cardiac cycle. The use of multi-ply struts enables theleaflets to be sandwiched in between the struts, which re-enforces theleaflet attachments and prevents tearing of sutures. The valve furtherassumes a desirable leaflet morphology, which further reduces the stressand strain on leaflets. Namely, the angled leaflet attachment to thestent is similar to the native human aortic valve's inter-leaflettrigone pattern. These properties significantly improve the longevity ofpercutaneous heart valve replacement therapies.

The device could reduce or eliminate arrthymia complications due to theincremental expansion or compression of the stent. The stent can employa screw mechanism for deployment, which enables the stent to self-lockor un-lock at all radii. This enables more controlled deployment and thepotential for individualizing the expansion or compression of the devicein each patient. Because the expansion or compression of the device isreversible at any stage during the procedure, the surgeon can easilyreverse the expansion of the device to relieve an arrythmia. Inaddition, if an arrythmia is detected during implantation, the devicecan be repositioned to further eliminate the problem.

The device can reduce or eliminate paravalvular leak due to the device'sability to be accurately positioned, and re-positioned, if necessary.That can considerably decrease the occurance and severity of paravalularleaks.

The device eliminates balloon-related complications. The screw mechanismof deployment exploits the mechanical advantage of a screw. Thisprovides for forceful dilation of the stent. The lever arms created bythe pivoting of the struts in the scissor linkage of the stent,transmits a further expansion force to the stent. The stent is expandedwithout the need for a balloon. In addition, the ability of the deviceto be forcefully dilated reduces or eliminates the need for pre- orpostballooning during the implantation procedure in patients.

The device has more predictable and precise positioning in the bodybecause the difference between the height of the stent in the compressedand expanded position is small. This “reduced foreshortening” helps thesurgeon to position the device in the desirable location in the body.The ability to re-position the device in the body further confers theability to precisely position the device in each individual.

In addition to the mechanical advantages, the device enables a widerpopulation of patients to be treated by a less invasive means for valvereplacement. For example, the device enables patients withco-morbidites, whom are not candidates for open chest surgical valvereplacement, to be offered a treatment option. The device's ability toassume a narrow profile also enables patients who were previously deniedtreatment due to poor vascular access (e.g. tortuous, calcified, orsmall arteries), to be offered a treatment option. The durability of thevalve should expand the use of less-invasive procedures to thepopulation of otherwise healthy patients, whom would otherwise becandidates for open chest surgical valve replacement. The device'sability to be forcefully expanded, or assume hourglass, or conicalshapes, potentially expands the device application to the treatment ofpatients diagnosed with aortic insufficiency, as well as aorticstenosis.

The device can also provide a less invasive treatment to patients withdegenerative prosthesis from a prior implant, by providing for a“valve-in-valve” procedure. The device could be accurately positionedinside the failing valve, without removing the patient's degenerativeprosthesis. It would help the patient by providing a functional valvereplacement, without a “re-do” operation and its associated risks.

While this invention has been particularly shown and described withreferences to particular embodiments, it will be understood by thoseskilled in the art that various changes in form and details may be madeto the embodiments without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A method of fabricating a support apparatusimplantable within a biological lumen, comprising: interlinking aplurality of strut members with a plurality of swivel joints, theplurality of strut members comprising a plurality of inner strut membersand a plurality of outer strut members, without directly interlinkingany of the inner strut members to each other by swivel joints, andwherein each of the plurality of inner strut members and each of theplurality of outer strut members is directly interlinked to three otherstrut members of the plurality of strut members by swivel joints, suchthat the swivel joints cooperate with the strut members to adjustablydefine a tubular shaped structure between a compressed orientation andan expanded orientation, wherein the tubular shaped structure has alongitudinal axis, and wherein each of the plurality of inner strutmembers in its entirety is closer to the longitudinal axis than each ofthe outer strut members.
 2. The method of claim 1, further comprisingcoupling an actuation mechanism to the shaped structure to urge theswivel joints within a range of motion.
 3. The method of claim 2,wherein the method comprises coupling the actuation mechanism to thestrut members.
 4. A method of fabricating a medical stent implantablewithin a biological lumen, comprising: fabricating a plurality ofelongated strut members, including a plurality of outer strut membersand a plurality of inner strut members; and connecting each of theplurality of inner strut members and each of the plurality of outerstrut members with three other strut members of the plurality ofelongated strut members with swivel joints, without directlyinterlinking any of the inner strut members to each other with a swiveljoint, to form a tubular shaped structure having a longitudinal axis,wherein each of the plurality of inner strut members in its entirety iscloser to the longitudinal axis than each of the outer strut members. 5.The method of claim 4, further comprising coupling an adjustmentmechanism to at least one of the inner and at least one of the outerstrut members to exert a force to urge the inner and outer strut membersabout the plurality of swivel joints within a range of motion.